U.S. patent application number 15/374490 was filed with the patent office on 2018-06-14 for display device system with tilted lens group to prevent ghost images.
The applicant listed for this patent is Dmitry Reshidko, R. Andrew Wall. Invention is credited to Dmitry Reshidko, R. Andrew Wall.
Application Number | 20180164583 15/374490 |
Document ID | / |
Family ID | 60766187 |
Filed Date | 2018-06-14 |
United States Patent
Application |
20180164583 |
Kind Code |
A1 |
Wall; R. Andrew ; et
al. |
June 14, 2018 |
DISPLAY DEVICE SYSTEM WITH TILTED LENS GROUP TO PREVENT GHOST
IMAGES
Abstract
A display device system includes a display engine and optical
waveguide. The display engine includes an image former, that
produces light corresponding to an image, and one or more lens
groups that collimate the light corresponding to the image and
outputs the light from the display engine. Each lens group includes
one or more lenses that share a mechanical axis. The light
corresponding to the image produced by the image former has an
optical axis ray coincident with a principal ray of the light that
originates at a center of the image produced by the image former.
At least one lens group has its mechanical axis tilted relative to
the optical axis ray of the light corresponding to the image
produced by the image former, to prevent a ghost image from being
formed by light corresponding to the image that is reflected-back
from the waveguide toward the display engine.
Inventors: |
Wall; R. Andrew; (Kirkland,
WA) ; Reshidko; Dmitry; (Tucson, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wall; R. Andrew
Reshidko; Dmitry |
Kirkland
Tucson |
WA
AZ |
US
US |
|
|
Family ID: |
60766187 |
Appl. No.: |
15/374490 |
Filed: |
December 9, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 27/1086 20130101;
G02B 27/0018 20130101; G02B 2027/012 20130101; G02B 27/30 20130101;
G02B 6/0016 20130101; G02B 27/0172 20130101 |
International
Class: |
G02B 27/00 20060101
G02B027/00; F21V 8/00 20060101 F21V008/00; G02B 27/10 20060101
G02B027/10; G02B 27/01 20060101 G02B027/01; G02B 27/30 20060101
G02B027/30 |
Claims
1. A see-through, mixed reality display device system, comprising:
a display engine including an image former and one or more lens
groups; the image former configured to produce light corresponding
to an image; and the one or more lens groups configured to
collimate the light corresponding to the image, produced by the
image former, and thereafter output the light corresponding to the
image from the display engine; wherein each lens group, of the one
or more lens groups, includes one or more lenses; and wherein if a
said lens group includes a plurality of lenses, the plurality of
lenses of the lens group share a same mechanical axis; an optical
waveguide including a bulk-substrate, an input-coupler and an
output-coupler, and configured to combine the light corresponding
to the image that is output from the display engine with light
corresponding to an external scene; wherein the light corresponding
to the image that is produced by the image former has an optical
axis ray, which is coincident with a principal ray of the light
that originates at a center of the image produced by the image
former; wherein the image former, the one or more lens groups, and
the optical waveguide are positioned relative to one another such
that a portion of the light corresponding to the image that is
output from the display engine is reflected-back toward the display
engine; and wherein at least one lens group, of the one or more
lens groups of the display engine, has a mechanical axis that is
tilted relative to the optical axis ray of the light corresponding
to the image that is produced by the image former, and is/are
thereby configured to prevent a ghost image from being formed by
the light corresponding to the image that is reflected-back toward
the display engine.
2. The display system of claim 1, wherein: the bulk-substrate of
the optical waveguide including a first major side and a second
major side opposite the first major side; the input-coupler of the
optical waveguide is configured to couple, into the bulk-substrate
of the optical waveguide, light corresponding to the image that is
output by the display engine; and the output-coupler of the optical
waveguide is configured to couple, out of the bulk-substrate of the
optical waveguide, light corresponding to the image that after
being coupled into the bulk-substrate of the optical waveguide has
traveled through the optical waveguide from the input-coupler to
the output-coupler at least in part by way of total internal
reflection (TIR).
3. The display system of claim 1, wherein the input-coupler
comprises a diffraction grating.
4. The display system of claim 1, wherein: the image former, the
one or more lens groups, and the optical waveguide are positioned
relative to one another such that a portion of the light
corresponding to the image that is reflected-back toward the
display engine is incident on the image former; and the at least
one lens group, that has a mechanical axis that is tilted relative
to the optical axis ray of the light corresponding to the image
that is produced by the image former, prevents a ghost image from
being formed by preventing the reflected-back portion of the light
corresponding to the image from being incident on the input-coupler
after being reflected from the image former.
5. The display system of claim 1, wherein: the optical waveguide
also includes an intermediate-component; the input-coupler is
configured to direct the light corresponding to the image, which is
output by the display engine and is coupled into the bulk-substrate
of the optical waveguide, toward the intermediate-component; the
intermediate-component is configured to perform one of horizontal
or vertical pupil expansion and to direct the light corresponding
to the image towards the output-coupler; and the output-coupler is
configured to perform the other one of horizontal or vertical pupil
expansion.
6. The display system of claim 1, wherein the at least one lens
group, that has a mechanical axis that is tilted relative to the
optical axis ray of the light corresponding to the image that is
produced by the image former, prevents a ghost image from being
formed by preventing the reflected-back portion of the light
corresponding to the image from being retro-reflected relative to
the light corresponding to the image that is incident on the
optical waveguide after being output by the display engine.
7. The display system of claim 1, wherein the one or more lens
groups includes at least two lens groups that each have a
mechanical axis that is tilted relative to the optical axis ray of
the light corresponding to the image that is produced by the image
former.
8. The display system of claim 1, wherein the one or more lens
groups includes a single lens group, the single lens group having a
mechanical axis that is tilted relative to the optical axis ray of
the light corresponding to the image that is produced by the image
former.
9. The display system of claim 1, wherein the display engine
further comprises: one or more optical elements that is/are
configured to steer or fold the optical axis ray of the light
corresponding to the image that is produced by the image former,
wherein the one or more optical elements is/are selected from a
group consisting of a beam splitter, a fold mirror and a birdbath
optical element.
10. The display system of claim 1, wherein the image former
comprises a liquid crystal on silicon (LCoS) microdisplay.
11. For use in display device system that includes a display engine
and an optical waveguide, a method for preventing a ghost image
from being formed by light corresponding to an image that is
reflected-back toward the display engine from the optical
waveguide, wherein the display engine includes an image former and
one or more lens groups, wherein each lens group of the one or more
lens groups including one or more lenses, wherein if a said lens
group includes a plurality of lenses the plurality of lenses of the
lens group share a same mechanical axis, and wherein the optical
waveguide includes an input-coupler and an output-coupler, the
method comprising: producing light corresponding to an image using
the image former of the display engine, wherein the light
corresponding to the image that is produced by the image former has
an optical axis ray which is coincident with a principal ray of the
light that originates at a center of the image produced by the
image former; and using the one or more lens groups of the display
engine to collimate the light corresponding to the image, produced
by the image former, and to output the light corresponding to the
image from the display engine, wherein at least one of the lens
group of the display engine has a mechanical axis that is tilted
relative to the optical axis ray of the light corresponding to the
image that is produced by the image former; coupling into the
optical waveguide, using the input-coupler, light corresponding to
the image that is output by the display engine; coupling out of the
optical waveguide, using the output coupler, light corresponding to
the image that that has traveled through the optical waveguide from
the input-coupler to the output-coupler at least in part by way of
total internal reflection (TIR); and using at least one of the lens
group of the display engine, which has a mechanical axis that is
tilted relative to the optical axis ray of the light corresponding
to the image that is produced by the image former, to prevent a
ghost image from being formed by the light corresponding to the
image that is reflected-back toward the display engine from the
optical waveguide.
12. The method of claim 11, wherein the one or more lens groups
includes at least two lens groups that each have a mechanical axis
that is tilted relative to the optical axis ray of the light
corresponding to the image that is produced by the image
former.
13. The method of claim 11, wherein the one or more lens groups
includes a single lens group, the single lens group having a
mechanical axis that is tilted relative to the optical axis ray of
the light corresponding to the image that is produced by the image
former.
14. The method of claim 11, wherein the image former comprises a
liquid crystal on silicon (LCoS) microdisplay.
15. The method of claim 11, further comprising combining the light
corresponding to the image that is output from the display engine
with light corresponding to an external scene, the combining
performing using the optical waveguide.
16. A see-through, mixed reality display device system, comprising:
a display engine including an image former and one or more lens
groups; the image former configured to produce light corresponding
to an image; and the one or more lens groups configured to
collimate the light corresponding to the image, produced by the
image former, and thereafter output the light corresponding to the
image from the display engine; wherein each lens group, of the one
or more lens groups, includes one or more lenses; and wherein if a
said lens group includes a plurality of lenses, the plurality of
lenses of the lens group share a same mechanical axis; an optical
waveguide including a bulk-substrate, an input-coupler and an
output-coupler; the bulk-substrate of the optical waveguide
including a first major side and a second major side opposite the
first major side; the input-coupler of the optical waveguide
configured to couple, into the bulk-substrate of the optical
waveguide, light corresponding to the image that is output by the
display engine; and the output-coupler of the optical waveguide
configured to couple, out of the bulk-substrate of the optical
waveguide, light corresponding to the image that after being
coupled into the bulk-substrate of the optical waveguide has
traveled through the optical waveguide from the input-coupler to
the diffractive output-coupler at least in part by way of total
internal reflection (TIR); wherein the light corresponding to the
image that is produced by the image former has an optical axis ray,
which is coincident with a principal ray of the light that
originates at a center of the image produced by the image former;
wherein the image former, the one or more lens groups, and the
optical waveguide are positioned relative to one another such that
a portion of the light corresponding to the image that is output
from the display engine is reflected-back toward the display
engine; and wherein at least one lens group, of the one or more
lens groups of the display engine, has a mechanical axis that is
tilted relative to the optical axis ray of the light corresponding
to the image that is produced by the image former.
17. The display system of claim 16, wherein: the optical waveguide
also includes an intermediate-component; the input-coupler is
configured to direct the light corresponding to the image, which is
output by the display engine and is coupled into the bulk-substrate
of the optical waveguide, toward the intermediate-component; the
intermediate-component is configured to perform one of horizontal
or vertical pupil expansion and to direct the light corresponding
to the image towards the output-coupler; and the output-coupler is
configured to perform the other one of horizontal or vertical pupil
expansion.
18. The display system of claim 16, wherein: the image former, the
one or more lens groups, and the optical waveguide are positioned
relative to one another such that the portion of the light
corresponding to the image that is reflected-back toward the
display engine is incident on the image former; and the at least
one lens group, that has a mechanical axis that is tilted relative
to the optical axis ray of the light corresponding to the image
that is produced by the image former, is/are configured to prevent
a ghost image from being formed by preventing the reflected-back
portion of the light corresponding to the image from being incident
on the input-coupler after being reflected from the image
former.
19. The display system of claim 16, wherein the at least one lens
group, that has a mechanical axis that is tilted relative to the
optical axis ray of the light corresponding to the image that is
produced by the image former, is/are configured to prevent a ghost
image from being formed by preventing the reflected-back portion of
the light corresponding to the image from being retro-reflected
relative to the light corresponding to the image that is incident
on the input-coupler of the optical waveguide after being output by
the display engine.
20. The display system of claim 16, wherein the one or more lens
groups includes at least two lens groups that each have a
mechanical axis that is tilted relative to the optical axis ray of
the light corresponding to the image that is produced by the image
former.
Description
BACKGROUND
[0001] Various types of computing, entertainment, and/or mobile
devices can be implemented with a transparent or semi-transparent
display through which a user of a device can view the surrounding
environment. Such devices, which can be referred to as see-through,
mixed reality display device systems, or as augmented reality (AR)
systems, enable a user to see through the transparent or
semi-transparent display of a device to view the surrounding
environment, and also see images of virtual objects (e.g., text,
graphics, video, etc.) that are generated for display to appear as
a part of, and/or overlaid upon, the surrounding environment. These
devices, which can be implemented as head-mounted display (HMD)
glasses or other wearable display devices, but are not limited
thereto, often utilize optical waveguides to replicate an image,
e.g., produced by a display engine, to a location where a user of a
device can view the image as a virtual image in an augmented
reality environment. As this is still an emerging technology, there
are certain challenges associated with utilizing waveguides to
display images of virtual objects to a user.
SUMMARY
[0002] Certain embodiments of the present technology related to
apparatuses, methods and systems for mitigating ghost images in
see-through, mixed reality display device systems are described
herein. In accordance with an embodiment, a see-through, mixed
reality display device system includes a display engine and an
optical waveguide. The display engine includes an image former and
one or more lens groups. The image former (e.g., a liquid crystal
on silicon (LCoS) microdisplay, but not limited thereto) of the
display engine is configured to produce light corresponding to an
image. The one or more lens groups of the display engine is/are
configured to collimate the light corresponding to the image,
produced by the image former, and thereafter output the light
corresponding to the image from the display engine. Each lens
group, of the one or more lens groups of the display engine,
includes one or more lenses. If a lens group includes multiple
lenses, the lenses of the lens group share a same mechanical axis.
In accordance with certain embodiments, optical waveguide is
configured to combine the light corresponding to the image that is
output from the display engine with light corresponding to an
external scene. The light corresponding to the image that is
produced by the image former has an optical axis ray, which is
coincident with a principal ray of the light that originates at a
center of the image produced by the image former. The image former,
the one or more lens groups, and the optical waveguide are
positioned relative to one another such that a portion of the light
corresponding to the image that is output from the display engine
is reflected-back toward the display engine. In accordance with
certain embodiments, at least one lens group, of the one or more
lens groups of the display engine, has a mechanical axis that is
tilted relative to the optical axis ray of the light corresponding
to the image that is produced by the image former, and is/are
thereby configured to prevent a ghost image from being formed by
the light corresponding to the image that is reflected-back toward
the display engine.
[0003] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIGS. 1A, 1B and 1C are front, top and side views,
respectively, of an exemplary optical waveguide that can be used to
replicate an image associated with an input-pupil to an expanded
output-pupil.
[0005] FIG. 2 is side view of an exemplary see-through, mixed
reality display system that includes an optical waveguide (which is
the same or similar to the waveguide introduced with reference to
FIGS. 1A, 1B and 1C) and a display engine that generates an image
including angular content that is coupled into the waveguide by an
input-coupler. FIG. 2 also shows an eye that is viewing the image
within an eye box that is proximate the output-coupler. FIG. 2 also
shows how a ghost image can be caused by light that is
reflected-back from the optical waveguide toward the display
engine.
[0006] FIG. 3 is a side view that is similar to FIG. 2, but shows a
lens group (within the display engine) having a mechanical axis
that is tilted relative to an optical axis ray of light that is
output from the image former, in accordance with an embodiment of
the present technology.
[0007] FIG. 4 is a side view that is similar to FIGS. 2 and 3, but
shows two lens groups (within the display engine) each having their
mechanical axis tilted relative to an optical axis ray of light
that is output from the image former, in accordance with an
embodiment of the present technology.
[0008] FIG. 5 is a side view that is similar to FIGS. 2-4, but
shows how the display engine can include a mirror or beam splitter
that steers or folds the light (including the optical axis ray)
corresponding to the image that is produced by the image former.
FIG. 5 also shows a lens group (within the display engine) having a
mechanical axis that is tilted relative to an optical axis ray of
light that is output from the image former, in accordance with an
embodiment of the present technology.
[0009] FIG. 6 is a high level flow diagram that is used to
summarize methods according to certain embodiments of the present
technology.
DETAILED DESCRIPTION
[0010] Certain embodiments of the present technology, as noted
above, related to apparatuses, methods and systems for mitigating
ghost images in see-through, mixed reality display device systems
that include a display engine and an optical waveguide.
[0011] In the description that follows, like numerals or reference
designators will be used to refer to like parts or elements
throughout. In addition, the first digit of a three digit reference
number identifies the drawing in which the reference number first
appears.
[0012] FIGS. 1A, 1B and 1C are front, top and side views,
respectively, of an exemplary optical waveguide 102 that can be
used to replicate an image associated with an input-pupil to an
expanded output-pupil. The term "input-pupil," as used herein,
refers to an aperture through which light corresponding to an image
is overlaid on an input-coupler of a waveguide. The term
"output-pupil," as used herein, refers to an aperture through which
light corresponding to an image exits an output-coupler of a
waveguide. An input-pupil is sometimes also referred to as an
entrance-pupil, and an output-pupil is sometimes also referred to
as an exit-pupil. The optical waveguide 102 will often be referred
to hereafter more succinctly simply as a waveguide 102. As will be
discussed in further detail below with reference to FIG. 2, the
image that the waveguide 102 is being used to replicate, and likely
also expand, can be generated using a display engine. When used
within a see-through, mixed reality display device system, the
waveguide 102 can be used as an optical combiner that is configured
to combine the light corresponding to a virtual image (that is
output from a display engine) with light corresponding to an
external scene. Where the waveguide relies on diffractive optical
elements to couple light into the waveguide and/or out of the
waveguide, the waveguide may be referred to as a diffractive
waveguide. Such a diffractive waveguide can be used as a
diffractive optical combiner.
[0013] Referring to FIGS. 1A, 1B and 1C, the optical waveguide 102
includes a bulk-substrate 106 having an input-coupler 112 and an
output-coupler 116. The input-coupler 112 is configured to couple
light corresponding to an image associated with an input-pupil into
the bulk-substrate 106 of the waveguide. The output-coupler 116 is
configured to couple the light corresponding to the image
associated with the input-pupil, which travels in the optical
waveguide 102 from the input-coupler 112 to the output-coupler 116,
out of the waveguide 102 so that the light is output and viewable
from the output-pupil.
[0014] The bulk-substrate 106, which can be made of glass or
optical plastic, but is not limited thereto, includes a first major
side 108, a second major side 110, and peripheral sides 109a, 109b,
109c and 109d. The first major side 108 and the second major side
110 are opposite and parallel to one another. In accordance with
certain embodiments, the major sides 108 and 110 are planar. In
accordance with other embodiments, the major sides 108 and 110 are
curved. The first major side 108 can alternatively be referred to
as the front-side 108, and the second major side 110 can
alternatively be referred to as the back-side 110. The peripheral
sides 109a, 109b, 109c and 109d can be referred to individually as
a peripheral side 109, or collectively as the peripheral sides 109.
As the term "bulk" is used herein, a substrate is considered to be
"bulk" substrate where the thickness of the substrate (between its
major sides) is at least ten times (i.e., 10.times.) the wavelength
of the light for which the substrate is being used as an optical
transmission medium. For an example, where the light (for which the
substrate is being used as an optical transmission medium) is red
light having a wavelength of 620 nm, the substrate will be
considered a bulk-substrate where the thickness of the substrate
(between its major sides) is at least 6200 nm, i.e., at least 6.2
.mu.m. In accordance with certain embodiments, the bulk-substrate
106 has a thickness of at least 25 .mu.m between its major sides
108 and 110. In specific embodiments, the bulk-substrate 106 has a
thickness (between its major sides) within a range of 25 .mu.m to
1020 .mu.m. The bulk-substrate 106, and more generally the
waveguide 102, is transparent, meaning that it allows light to pass
through it so that a user can see through the waveguide 102 and
observe objects on an opposite side of the waveguide 102 than the
user's eye(s).
[0015] The optical waveguide 102 in FIGS. 1A, 1B and 1C is also
shown as including an intermediate-component 114, which can
alternatively be referred to as an intermediate-zone 114. Where the
waveguide 102 includes the intermediate-component 114, the
input-coupler 112 is configured to couple light into the waveguide
102 (and more specifically, into the bulk-substrate 106 of the
waveguide 102) and in a direction of the intermediate-component
114. The intermediate-component 114 is configured to redirect such
light in a direction of the output-coupler 116. Further, the
intermediate-component 114 is configured to perform one of
horizontal or vertical pupil expansion, and the output-coupler 116
is configured to perform the other one of horizontal or vertical
pupil expansion. For example, the intermediate-component 114 can be
configured to perform horizontal pupil expansion, and the
output-coupler 116 can be configured to vertical pupil expansion.
Alternatively, if the intermediate-component 114 were repositioned,
e.g., to be below the input-coupler 112 and to the left of the
output-coupler 116 shown in FIG. 1A, then the
intermediate-component 114 can be configured to perform vertical
pupil expansion, and the output-coupler 116 can be configured to
perform horizontal pupil expansion.
[0016] The input-coupler 112, the intermediate-component 114 and
the output-coupler 116 can be referred to collectively herein as
optical components 112, 114 and 116 of the waveguide, or more
succinctly as components 112, 114 and 116. Where the optical
components 112, 114 and 116 are diffractive gratings, they can be
referred to as diffractive optical elements (DOEs) 112, 114 and
116, or more specifically, as a diffractive input-coupler 112, a
diffractive intermediate-component 114 and a diffractive
output-coupler 116.
[0017] It is possible that a waveguide includes an input-coupler
and an output-coupler, without including an
intermediate-components. In such embodiments, the input-coupler
would be configured to couple light into the waveguide and in a
direction toward the output-coupler. In such embodiments, the
output-coupler can provide one of horizontal or vertical pupil
expansion, depending upon implementation.
[0018] In FIG. 1A, the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 are shown as
having rectangular outer peripheral shapes, but can have
alternative outer peripheral shapes. For example, the input-coupler
112 can alternatively have a circular outer peripheral shape, but
is not limited thereto. For another example, the
intermediate-component can have a triangular or hexagonal outer
peripheral shape, but is not limited thereto. Further, it is noted
that the corners of each of the peripheral shapes, e.g., where
generally rectangular or triangular, can be chamfered or rounded,
but are not limited thereto. These are just a few exemplary outer
peripheral shapes for the input-coupler 112, the
intermediate-component 114 and the output-coupler 116, which are
not intended to be all encompassing.
[0019] As can best be appreciated from FIGS. 1B and 1C, the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 are all shown as being provided in or on a same
side (i.e., the back-side 110) of the waveguide 102. In such a
case, the input-coupler 112 can be transmissive (e.g., a
transmission grating), the intermediate-component 114 can be
reflective (e.g., a reflective grating), and the output-coupler 116
can also be reflective (e.g., a further reflective grating). The
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 can alternatively all be provided in the
front-side 110 of the waveguide 102. In such a case, the
input-coupler 112 can be reflective (e.g., a reflective grating),
the intermediate-component 114 can be reflective (e.g., a further
reflective grating), and the output-coupler 116 can also be
transmissive (e.g., a transmission grating).
[0020] Alternatively, the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 can all be
embedded (also referred to as immersed) in the bulk-substrate 106.
For example, the bulk-substrate 106 can be separated into two
halves (that are parallel to the major sides 108 and 110), and the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 can be provided in (e.g., etched into) one of
the inner surfaces of the two halves, and the inner surfaces of the
two halves can be adhered to one another. Alternatively, the
bulk-substrate 106 can be separated into two halves (that are
parallel to the major sides 108 and 110), and the input-coupler
112, the intermediate-component 114 and the output-coupler 116 can
be provided between the inner surfaces of the two halves. Other
implementations for embedding the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 in the
bulk-substrate 106 are also possible, and within the scope of the
embodiments described herein. It is also possible that one of the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 is provided in or on the front-side 108 of the
waveguide 102, another one of the components 112, 114 and 116 is
provided in or on the back-side 110, and the last one of the
components 112, 114 and 116 is embedded or immersed in the
bulk-substrate 106. More generally, unless stated otherwise, any
individual one of the input-coupler 112, the intermediate-component
114 and the output-coupler 116 can be provided in or on either one
of the major sides 108 or 110 of the bulk-substrate 106, or
embedded therebetween.
[0021] As noted above, the input-coupler 112, the
intermediate-component 114 and the output-coupler 116 can each be
implemented as a diffraction grating, or more generally, as a
diffractive optical element (DOE). A diffraction grating is an
optical component that may contain a periodic structure that causes
incident light to split and change direction due to an optical
phenomenon known as diffraction. The splitting (known as optical
orders) and angle change depend on the characteristics of the
diffraction grating. When the periodic structure is on the surface
of an optical component, it is referred to a surface grating. When
the periodic structure is due to varying of the surface itself, it
is referred to as a surface relief grating (SRG). For example, an
SRG can include uniform straight grooves in a surface of an optical
component that are separated by uniform straight groove spacing
regions. Groove spacing regions can be referred to as "lines",
"grating lines" or "filling regions". The nature of the diffraction
by an SRG depends on the wavelength, polarization and angle of
light incident on the SRG and various optical characteristics of
the SRG, such as refractive index (also known as the index of
refraction), line spacing, groove depth, groove profile, groove
fill ratio and groove slant angle. An SRG can be fabricated by way
of a suitable microfabrication process, which may involve etching
of and/or deposition on a substrate to fabricate a desired periodic
microstructure on the substrate to form an optical component, which
may then be used as a production master such as a mold or mask for
manufacturing further optical components. An SRG is an example of a
Diffractive Optical Element (DOE). When a DOE is present on a
surface (e.g. when the DOE is an SRG), the portion of that surface
spanned by that DOE can be referred to as a DOE area. A diffraction
grating, instead of being a surface grating, can alternatively be a
volume grating, such as a Bragg diffraction grating. It is also
possible that one or more of the couplers are manufactured as SRGs
and then covered within another material, e.g., using an aluminum
deposition process, thereby essentially burying the SRGs such that
the major waveguide surface(s) including the SRG(s) is/are
substantially smooth. Such a coupler is one example of a hybrid of
a surface and volume diffraction grating. Any one of the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 can be, e.g., a surface diffraction grating, or
a volume diffraction grating, or a hybrid of a surface and volume
diffraction grating. Each diffraction grating can have a
preferential linear polarization orientation specified by a
direction of the grating lines of the diffraction grating, wherein
the coupling efficiency for light having the preferential linear
polarization orientation will be higher than for light having a
non-preferential linear polarization orientation.
[0022] Where the input-coupler 112, the intermediate-component 114
and/or the output-coupler 116 is an SRG, each such SRG can be
etched into one of the major sides 108 or 110 of the bulk-substrate
106. In such embodiments, the SRG can be said to be formed "in" the
bulk-substrate 106. Alternatively, each SRG can be physically
formed in a coating that covers one of the major sides 108 or 110
of the bulk-substrate 106, in which case each such SRG can be said
to be formed "on" the bulk-substrate 106. Either way, the
components 112, 114 and 116 are considered parts of the waveguide
102.
[0023] Referring specifically to FIG. 1A, in an exemplary
embodiment, the input-coupler 112 can have surface gratings that
extend in a vertical (y) direction, the output-coupler 116 can have
surface gratings that extend in a horizontal (x) direction, and the
intermediate-component 114 can have surface gratings that extend
diagonal (e.g., .about.45 degrees) relative to the horizontal and
vertical directions. This is just an example. Other variations are
also possible.
[0024] The input-coupler 112 can alternatively be implemented as a
prism, a reflective polarizer or can be mirror based. Similarly,
the output-coupler 116 can alternatively be implemented as a prism,
a reflective polarizer or can be mirror based. Depending upon the
specific configuration and implementation, any one of the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 can be reflective, diffractive or refractive, or
a combination thereof, and can be implemented, e.g., as a linear
grating type of coupler, a holographic grating type of coupler, a
prism or another type of optical coupler. The
intermediate-component 114 can be implemented using a fold-grating,
or can alternatively be implemented as a mirror based pupil
expander, but is not limited thereto. More generally, the
input-coupler 112, the intermediate-component 114 and the
output-coupler 116 can have various different outer peripheral
geometries, can be provided in or on either of the major sides of
the bulk-substrate, or can be embedded in the bulk-substrate 106,
and can be implemented using various different types of optical
structures, as can be appreciated from the above discussion, and
will further be appreciated from the discussion below.
[0025] In general, light corresponding to an image, which is
coupled into the waveguide via the input-coupler 112, can travel
through the waveguide from the input-coupler 112 to the
output-coupler 116, by way of total internal refection (TIR). TIR
is a phenomenon which occurs when a propagating light wave strikes
a medium boundary (e.g., of the bulk-substrate 106) at an angle
larger than the critical angle with respect to the normal to the
surface. In other words, the critical angle (.theta..sub.c) is the
angle of incidence above which TIR occurs, which is given by
Snell's Law, as is known in the art. More specifically, Snell's law
specifies that the critical angle (.theta..sub.c) is specified
using the following equation:
.theta..sub.c=sin.sup.-1(n2/n1)
where
[0026] .theta..sub.c the critical angle for two optical mediums
(e.g., the bulk-substrate 106, and air or some other medium that is
adjacent to the bulk-substrate 106) that meet at a medium
boundary,
[0027] n1 is the index of refraction of the optical medium in which
light is traveling towards the medium boundary (e.g., the
bulk-substrate 106, once the light is couple therein), and
[0028] n2 is the index of refraction of the optical medium beyond
the medium boundary (e.g., air or some other medium adjacent to the
bulk-substrate 106).
[0029] The concept of light traveling through the waveguide 102,
from the input-coupler 112 to the output-coupler 116, by way of
TIR, can be better appreciated from FIG. 2, which is discussed
below. Referring now to FIG. 2, as in FIG. 1C, FIG. 2 shows a side
view of the waveguide 102, but also shows a display engine 204 that
generates an image including angular content that is coupled into
the waveguide by the input-coupler 112. Also shown in FIG. 2, is
representation of a human eye 214 that is using the waveguide 102
to observe an image, produced using the display engine 204, as a
virtual image. More generally, FIG. 2 shows an exemplary
see-through, mixed reality display system 200.
[0030] The display engine 204 can include, e.g., an image former
206 and one or more lens group 208, but is not limited thereto. For
example, the display engine 204 may also include an illuminator
(not shown). The image former 206 can be configured to produce
light corresponding to an image. The image former 206 can be
implemented using a reflective technology for which external light,
produced by an illuminator, is reflected and modulated by an
optically active material. Digital light processing (DLP), liquid
crystal on silicon (LCoS) and Mirasol.TM. display technology from
Qualcomm, Inc. are all examples of reflective technologies. Where
the image former 206 is an LCoS microdisplay, it includes a
reflective display surface including pixels that can be in an "on"
state or an "off" state, as controlled by electronics (not
shown).
[0031] The image former 206 can alternatively be implemented using
a transmissive projection technology where a light source is
modulated by an optically active material, and backlit with white
light. These technologies are usually implemented using liquid
crystal display (LCD) type displays with powerful backlights and
high optical energy densities. An illuminator (not shown) can
provide the aforementioned backlighting. Alternatively, the image
former 206 can be implemented using an emissive technology where
light is generated by a display, see for example, a PicoP.TM.
display engine from Microvision, Inc. Another example of emissive
display technology is a micro organic light emitting diode (OLED)
display. Companies such as eMagin.TM. and Microoled.TM. provide
examples of micro OLED displays. The image former 206, alone or in
combination with an illuminator, can also be referred to as a micro
display.
[0032] In FIG. 2, the display engine 204 is shown as including two
lens groups, namely a lens group 208a and a lens group 208b, which
can be collectively referred to as lens groups 208, or individually
as a lens group 208. In FIG. 2, each of the lens groups 208 is
represented by a single lens, but can actually include more than
one lens. Further, in FIG. 2, each of the lens groups 208 is
represented as a biconvex lens, but that is just for illustration.
Each lens group 208 can include additional and/or alternative
type(s) of lens(es), including, but not limited to, one or more
plano-convex, positive meniscus, negative meniscus, plano-concave,
biconvex and/or biconcave type lens, just to name a few. Where
there is more than one lens group 208, the lens group that is
closest to the image former 206 can be referred to as the rear lens
group, and the lens group that is furthest from the image former
206 can be referred to as the front lens group. Thus, in FIG. 2,
the lens group 208a can be referred to as the rear lens group, and
the lens group 208b can be referred to as the front lens group.
There may also be one or more intermediate lens groups
therebetween. It is also possible that the display engine 204
includes only a single lens group 208. In accordance with an
embodiment, an entry pupil associated with the waveguide 102 may be
approximately the same size as an exit pupil associated with the
image former 206, e.g., 5 mm or less in some embodiments, but is
not limited thereto.
[0033] The one or more lens group 208 can be arranged to receive a
diverging display image from the image former 206, to collimate the
display image, and to direct the collimated image toward the
input-coupler 112 of the waveguide 102. More generally, the one or
more lens groups 208 are configured to collimate light
corresponding to an image, produced by the image former 206, and
thereafter output the light corresponding to the image from the
display engine 204. Each lens group 208 includes one or more
lenses. If lens group 208 includes a plurality of lenses, the
plurality of lenses of the lens group share a same mechanical axis.
The mechanical axis is the centerline of the outer cylindrical edge
of a lens, or simply its geometrical axis. The mechanical axis
coincides with a rotating axis of a centering machine that edges
the lens to its final diameter during the manufacture of a lens. As
the term mechanical axis is used herein, if one or more portions of
a lens originally having a circular diameter is/are trimmed off the
lens (e.g., because the portion(s) are not used or needed to
collimate the light corresponding to the image, produced by the
image former 206, and not used or needed to output the light
corresponding to the image from the display engine 204) so as to
cause the lens to no longer have a circular diameter, the
mechanical axis will be considered to not have changed. In other
words, the mechanical axis of a trimmed lens will be considered to
be the geometric axis of the lens prior to it being trimmed.
[0034] In FIG. 2, the display engine 204 is shown as facing the
back-side 110 of the waveguide 102, and the eye 214 is shown as
facing the front-side 108 opposite and parallel to the back-side
110. This provides for a periscope type of configuration in which
light enters the waveguide on one side of the waveguide 102, and
exits the waveguide at an opposite side of the waveguide 102.
Alternatively, the input-coupler 112 and the output-coupler 116 can
be implemented in a manner such that the display engine 204 and the
eye 214 are proximate to and face a same major side (108 or
110).
[0035] The waveguide 102 can be incorporated into a see-through
mixed reality display device system, in which case it can function
as an optical combiner that combines light corresponding to the
image, that is output from the display engine 204, with light
corresponding to an external scene that is on the opposite side of
the waveguide than a user's eye. A separate instance of the
waveguide 102 and the display engine 204 can be provided for each
of the left and right eyes of a user. In certain embodiments, such
waveguide(s) 102 may be positioned next to or between see-through
lenses, which may be standard lenses used in eye glasses and can be
made to any prescription (including no prescription). Where a
see-through mixed reality display device system is implemented as
head-mounted display (HMD) glasses including a frame, the display
engine 204 can be located to the side of the frame so that it sits
near to a user's temple. Alternatively, the display engine 204 can
be located in a central portion of the HMD glasses that rests above
a nose bridge of a user. Other locations for the display engine 204
are also possible. In these instances, the user can also be
referred to as a wearer. Where there is a separate waveguide for
each of the left and right eyes of a user, there can be a separate
display engine for each of the waveguides, and thus, for each of
the left and right eyes of the user. One or more further adjacent
waveguides can be used to perform eye tracking based on infrared
light that is incident on and reflected from the user's eye(s) 214,
as is known in the art.
[0036] As shown in FIG. 2, light corresponding to an image that is
coupled into the waveguide 102 by the input-coupler 112, can travel
by way of TIR from the input-coupler 112 to the
intermediate-component 114, and by way of TIR from the
intermediate-component 114 to the output-coupler 116, where it
exits the waveguide 102. More specifically, a combination of
diffractive beam splitting and TIR within the waveguide 102 results
in multiple versions of an input beam of light being outwardly
diffracted from the output-coupler 116 in both the length and the
width of the output-coupler 116.
[0037] In FIG. 2, the solid arrowed line 222 is representative of
light corresponding to an image (and more specifically, the
principal ray thereof) that is output by the display engine 204 and
is incident on the input-coupler 112, which as noted above, can be
a diffractive input-coupler 112, such as an SRG. A portion of the
solid arrowed line that is between the image former 206 and the
rear lens group 208a, which is labelled 223, is representative of
an optical axis ray of the light corresponding to the image that is
produced by the image former 206. The optical axis ray 223 is
coincident with the principal ray of the light that originates at a
center of the image produced by the image former 206. The principal
ray, which originates at the center of the image produced by the
image former 206, extends through the center of the aperture stop
of the display engine 204, with the aperture stop being coincident
with the exit pupil of the display engine 204. In the configuration
shown in FIG. 2, each of the lens groups 208a, 208b has a
respective mechanical axis 225a, 225b that is coincident with and
parallel to the optical axis ray 223 of the light corresponding to
the image that is produced by the image former 206. As explained
above, the mechanical axis of a lens group 208 is the geometrical
axis of the one or more lenses in the lens group 208. As also
explained above, if one or more portions of a lens originally
having a circular diameter is/are trimmed off the lens (e.g.,
because the portion(s) are not used or needed to collimate the
light corresponding to the image, produced by the image former 206,
and not used or needed to output the light corresponding to the
image from the display engine 204) so as to cause the lens to no
longer have a circular diameter, the mechanical axis will be
considered to not have changed. In other words, the mechanical axis
of a trimmed lens will be considered to be the geometric axis of
the lens prior to it being trimmed.
[0038] Preferably, all of the light corresponding to an image
(represented by the solid arrowed line 222) that is output from the
display engine 204 is diffracted or otherwise input into the
optical waveguide 102 by the input-coupler 112, and travels by way
of TIR to the output-coupler 116, where the light (corresponding to
the image) is coupled out of the optical waveguide 102 so that the
image can be viewed by the human eye 214. However, what typically
occurs, is that a portion of the light corresponding to the image
that is output from the display engine 204 is reflected-back toward
the display engine 204 due to Fresnel reflection. The dashed
arrowed line 232 is presentative of the reflected-back light. In
certain configurations, the reflected-back light 232 may be
retro-reflected, meaning that the reflected-back light 232 follows
the exact same path that it followed on the way towards the
input-coupler 112, but in the opposite direction.
[0039] In FIG. 2, it is presumed that the reflected-back light 232
is retro-reflected in the direction from which the light 222 came.
However, the reflected-back light 232 is shown as having an
exaggerated linear displacement, so that light that is incident on
the input-coupler 112 is distinguishable (for discussion and
illustrative purposes) from the light that is reflected-back
therefrom. More specifically, the reflected-back light 232 is shown
as being vertically displaced from the incident light 222. In
reality, the reflected-back light 232, if retro-reflected and drawn
accurately, would actually completely overlap the incident light
222. However, because it would be difficult to draw overlapping
beams that are distinguishable from one another, beams 222 and 232
are shown as being linearly displaced from one another.
[0040] Still referring to FIG. 2, the reflected-back light 232 is
shown as passing back through the lens groups 208 and being
incident on the image former 206, and then being reflected off the
image former 206. The dashed arrowed line 234 is representative of
the reflected-back light 232 after it has been reflected off of the
image former 206. Where the image former 206 is implemented using a
reflective technology (e.g., as an LCoS microdisplay),
substantially all of the reflected-back light 232 that is incident
on the image former 206 will be reflected therefrom. Where the
image former 206 is implemented using other technologies (e.g., a
transmissive or emissive technology), at least some of the
reflected-back light 232 that is incident on the image former 206
will be reflected therefrom, but likely to a lesser degree than
would occur if the image former were implemented using a reflective
technology. Regardless of the type of image former 206, at least
some of the reflected-back light 232, after being incident on the
image former 206 can be reflected off of the image former 206 and
incident again on the input-coupler 112 of the waveguide 102, as
indicated by the dashed arrowed line 234. In FIG. 2 the light
represented by the dashed arrowed line 234 is shown as being
coupled into the waveguide 102 (or more specifically, the
bulk-substrate 106 thereof) and traveling at least in part by way
of TIR to the output-coupler 116, where the light represented by
the dashed arrowed line 234 is coupled out of the optical waveguide
102 and viewable by the human eye 232 as an undesirable ghost image
of a virtual image presented to a user's eye by the optical
waveguide. Such a ghost image is essentially a replica of the
desired virtual image that is offset in position and super imposed
on top of the desired virtual image. Some light that is output by
the display engine 204 may also be reflected-back towards the
display engine 204 because the light, after being diffracted into
the optical waveguide 102 by the input-coupler 112, internally
reflects off of a surface of the waveguide and is incident on the
input-coupler 112 and undesirably diffractively out-coupled by the
input-coupler 112 back into the display engine 204. Such light can
also cause an undesirable ghost image of a virtual image presented
to a user's eye by the optical waveguide.
[0041] One potential solution for eliminating (or at least
mitigating) ghost images would be to tilt the optical waveguide 102
relative to the display engine 104, such that that light that is
undesirably reflected-back and/or diffractively out-coupled from
the optical waveguide 102 (such as the light represented by the
dashed line 232) is reflected-back at such an angle, relative to
the display engine 104, that the light does not make it back to the
image former 206. However, there are limitations to that solution.
More specifically, tilting the optical waveguide 102 relative to
the display engine 104 can have the undesirable effect of limiting
the field of view (FOV) that can be achieved. Further, tilting the
optical waveguide 102 relative to the display engine 204 can
adversely affect the form factor and/or industrial design of the
resulting display system, which may be very important where the
display system is, for example, a head mounted near eye display
system. Additionally, there is only so far that the optical
waveguide 102 can be tilted relative to the display engine 104
before a diffractive input-coupler 112 will no longer meet design
constraints and TIR requirements. Moreover, it is more challenging
to align a tilted waveguide relative to an image former than it is
to align a non-tilted waveguide related to an image former. Certain
embodiments of the present technology, which are described below,
provide for a more eloquent solution for eliminating (or at least
mitigating) the above described ghost images. One such embodiment
will first be described with reference to FIG. 3. It is noted that
certain embodiments of the present technology do not necessary
overcome all of the limitations associated with the above described
potential embodiment where the optical waveguide 102 is tilted
relative to the display engine 104.
[0042] FIG. 3 shows a see-through, mixed reality display system 300
according to an embodiment of the present technology. In FIG. 3
(and FIGS. 4 and 5), components that are the same as in FIG. 1
and/or 2 are labelled the same, and thus, need not be described
again. Similarly, arrowed lines representing light that are the
same as in FIG. 2, are labelled the same, and thus, need not be
described again.
[0043] Referring to FIG. 3, the display engine 204 is shown as
including an image former 206 and a single lens group 208. As noted
above, the display engine 204 may also include an illuminator (not
shown) and/or other elements. Light corresponding to an image that
is produced by the image former 206 has an optical axis ray 223
that is coincident with a principal ray of the light that
originates at a center of the image produced by the image former
206. The image former 206, the lens group 208, and the optical
waveguide 102 are positioned relative to one another such that a
portion of the light 222 corresponding to the image that is output
from the display engine 204 is reflected-back toward the display
engine 204. The dashed arrowed line 232 is representative of the
reflected-back light. In this embodiment, the lens group 208 has a
mechanical axis 225 that is tilted relative to the optical axis ray
223 of the light 222 corresponding to the image that is produced by
the image former 206.
[0044] In FIG. 3, a majority of the light corresponding to an image
(represented by the solid arrowed line 222) that is output from the
display engine 204 is diffracted into the optical waveguide 102 by
the input-coupler 112, and travels by way of TIR to the
output-coupler 116, where the light (corresponding to the image) is
coupled out of the optical waveguide 102 so that the image can be
viewed by the human eye 214. However, a portion of the light 222 is
reflected-back toward the display engine 204, as represented by the
dashed arrowed line 232. In contrast to FIG. 2, the reflected-back
light 232 in FIG. 3 is not retro-reflected. Rather, the angle of
reflection of the reflected-back light 232 in FIG. 3 is equal to
the angle of incidence of the light 222 in the plane of the page
(i.e., the y-z plane). As can be appreciated from FIG. 3, an effect
of the lens group 208 having its mechanical axis 225 sufficiently
and appropriately tilted relative to the optical axis ray 223 of
the light 222 that is output from the image former 206 is that the
reflected-back light 232 is not incident on the image former 206,
and thus, does not cause a ghost image to be formed.
[0045] In an embodiment, the mechanical axis 225 of the lens group
208 is tilted relative to the optical axis ray 223 of the light 222
that is output from the image former 206 such that the
reflected-back light 232 (or at least a portion thereof) is
incident on the image former 206, but at an angle of incidence
relative to the image former 206 such that any reflected-back light
232 incident on the image former 206 is reflected from the image
former 206 in such a way that it is never coupled into the optical
waveguide 102, and thus, does not cause any ghost images. For
example, reflected-back light after being incident on the image
former 206 can be reflected away from the input-coupler 112, and
thus, never coupled into the optical waveguide 102.
[0046] In accordance with certain embodiments, certain mechanical
surfaces and/or other mechanical portions of the display engine 204
(e.g., such as a lens barrel) are painted or otherwise coated with
a light absorbing material to reduce and preferably prevent stray
light incident thereon from being reflected-back toward the image
former 206. One or more additional and/or alternative type of light
trap can be used to absorb light that is reflected-back toward the
display engine 204, so as to minimize and preferably prevent such
reflected-back light from being incident on the image former
206.
[0047] In the embodiment of FIG. 3, the display engine 204 was
shown as including only a single lens group 208, which itself can
include one or more lenses. As noted above, where the lens group
208 includes multiple lenses, the lenses within the same lens group
208 share the same mechanical axis. In other embodiments, the
display engine 204 includes two or more lens groups 208, as
described below with reference to FIG. 4.
[0048] FIG. 4 shows a see-through, mixed reality display system 400
according to an embodiment of the present technology. Referring to
FIG. 4, the display engine 204 is shown as including two lens
groups 208a and 208b, which can collectively be referred to as the
lens groups 208, or individually as a lens group 208. In the
embodiment of FIG. 4, each of the lens groups 208a, 208b has a
respective mechanical axis 225a, 225b that is tilted relative to
the optical axis ray 223 of the light corresponding to the image
that is produced by the image former 206. Alternatively, only one
of the two lens groups 208a or 208b can have a mechanical axis 225a
or 225b that is tilted relative to the optical axis ray 223 of the
light corresponding to the image that is produced by the image
former 206.
[0049] In the embodiment of FIG. 4, the lens groups 208a and 208b
are shown as being collectively arranged relative to the image
former 206 and the optical waveguide 202 so as to prevent the
reflected-back light, represented by the dashed arrowed line 232,
from being incident on the image former 206, to thereby prevent a
ghost image from being formed by the reflected-back light 232.
Alternatively, where at least one of the lens groups 208a or 208b
has a mechanical axis 225a or 225b that is tilted relative to the
optical axis ray 223 of the light corresponding to the image that
is produced by the image former 206, the lens groups 208a and 208b
can be collectively arranged relative to the image former 206 and
the optical waveguide 202, such that at least some reflected-back
light 232 is indeed incident on the image former 206. In this
latter embodiment, in order to prevent a ghost image from being
formed, the aforementioned components are arranged relative to one
another so as to prevent the reflected-back light 232, after being
incident on the image former 206 and reflected therefrom, from
being incident on the input-coupler 112 of the optical waveguide
102. In other words, the lens group(s) 208, at least one of which
has a mechanical axis that is tilted relative to the optical axis
ray of the light corresponding to the image that is produced by the
image former 206, are arranged to prevent a ghost image from being
formed by preventing the reflected-back portion of the light
corresponding to the image from being incident on the input-coupler
112 after being reflected from the image former 206.
[0050] Certain embodiments of the present technology that tilt the
mechanical axis of at least two lens groups (relative to the
optical axis ray of light corresponding to an image produced by an
image former) take advantage of the fact that aberrations induced
by tilting one lens group can be compensated by tilting another one
of the lens groups in the opposite direction, e.g., as shown in
FIG. 4.
[0051] In the drawings of FIGS. 3 and 4, the light corresponding to
an image that is produced by the image former 206 was shown as
being generally directed toward the input-coupler 112 of the
optical waveguide 102. In an actual implementation, due to space
constraints, it is likely that one or more optical elements, such a
beam splitter, a fold mirror and/or a birdbath optical element,
is/are used to steer or fold the light (including the optical axis
ray of the light) corresponding to the image that is produced by
the image former 206. In such an embodiment, at least one lens
group, of the one or more lens groups of the display engine, can
have a mechanical axis that is tilted relative to the optical axis
ray of the light corresponding to the image that is produced by the
image former, to thereby prevent a ghost image from being formed by
the light corresponding to the image that is reflected-back toward
the display engine. An example of one such embodiment is shown in
FIG. 5.
[0052] FIG. 5 shows a see-through, mixed reality display system 500
according to an embodiment of the present technology. Referring to
FIG. 5, the display engine 204 therein is shown as having a mirror
or beam splitter 502 that steers or folds the light (including the
optical axis ray 223) corresponding to the image that is produced
by the image former 206. In FIG. 5, the optical axis ray 223 is
shown as being folded in an orthogonal direction relative to the
direction from which the optical axis ray 223 is produced by the
image former 206, but that need not be the case. In other words,
the mirror or beam splitter 502 may have steered or folded the
light (including the optical axis ray 223) corresponding to the
image, that is produced by the image former 206, in or at an angle
that is less than or greater than ninety degrees.
[0053] The display engine 204 in FIG. 5 is shown as including a
rear lens group 208a that is optically upstream of the mirror or
beam splitter 502, and a front lens group 208b that is optically
downstream of the mirror or beam splitter 502. In FIG. 5 only the
front lens group 208b is shown as having a mechanical axis 225b
that is tilted relative to the optical axis ray 223 of the light
corresponding to the image that is produced by the image former
206, so as to prevent a ghost image from being formed by the
reflected-back light 232 that is directed toward the display engine
204. Alternatively, or additionally, the rear lens group 208a can
have its mechanical axis 225a tilted relative to the optical axis
ray 223 of the light corresponding to the image that is produced by
the image former 206, so as to prevent a ghost image from being
formed by the reflected-back light 232 that is directed toward the
display engine 204.
[0054] In FIGS. 2-5, the optical axis ray 223 of the light
corresponding to the image that is produced by the image former 206
was show as being normal to the major reflective (or emitting)
surface of the image former 206. However, that need not be the
case. Rather, the image former 206 can be configured to produce
(reflect or emit) light corresponding to an image that has an
optical ray axis that is not normal to the major surface of the
reflective (or emitting) surface of the image former 206. For
example, where the image former 206 is an LCoS microdisplay, light
corresponding to an image (including the optical axis ray) that is
produced by the LCoS microdisplay can be reflected by (and thereby
produced by) the LCoS microdisplay at an angle relative to the
major reflective surface of the LCoS microdisplay by arranging an
illuminator (not shown) at an acute angle relative to the
reflective surface of the LCoS microdisplay. In such embodiments,
at least one lens group, of the one or more lens groups of the
display engine, can have a mechanical axis that is tilted relative
to the optical axis ray of the light corresponding to the image
that is produced by the image former, to thereby prevent a ghost
image from being formed by the light corresponding to the image
that is reflected-back toward the display engine. In other words,
embodiments of the present technology can also be used to prevent
ghost images where the image former 206 produces (reflects or
emits) light corresponding to an image that has an optical ray axis
that is not normal to the major reflective (or emitting) surface of
the image former 206.
[0055] In FIGS. 2-5, the major reflective (or emitting) surface of
the image former 206 (which may be made up of smaller or faceted
surfaces) was shown as being parallel to the major surfaces 110 and
108 of the optical waveguide 102. In alternative embodiments, that
need not be the case. More specifically, it is also within the
scope of certain embodiments of the present technology that the
optical waveguide 102 (and more specifically, the major sides 108
and 110 thereof) be tilted relative to, and thus not parallel to,
the major reflective (or emitting) surface of the image former 206.
For example, in accordance with an embodiment, the optical
waveguide 102 (and more specifically, the major sides 108 and 110
thereof) is tilted relative to the major reflective (or emitting)
surface of the image former 206, and at least one lens group 208
(of one or more lens groups) of the display engine 204 has a
mechanical axis that is tilted relative to the optical axis ray of
the light corresponding to the image that is produced by the image
former, and is/are thereby configured to prevent a ghost image from
being formed by the light corresponding to the image that is
reflected-back toward the display engine.
[0056] In FIGS. 2-5, the optical axis ray 223 of the light
corresponding to the image that is produced by the image former 206
was show as passing through the geometric center of each lens group
208. In such embodiments, it can be assumed that each lens group
208 has an aperture that is centered relative to the optical axis
ray 223 of the light corresponding to the image that is produced by
the image former 206. In alternative embodiments, that need not be
the case. More specifically, it is also within the scope of certain
embodiments of the present technology that one or more lens group,
and/or an aperture thereof, be decentered relative to the optical
axis ray 223 of the light corresponding to the image that is
produced by the image former 206. The decentered lens group (and/or
lens group having a decentered aperture) can be, but need not be,
the same lens group 208 that has its mechanical axis tilted
relative to the optical axis ray of the light corresponding to the
image that is produced by the image former 206. Where there are
multiple lens groups 208, one or more lens group can be decentered,
while one or more other lens group(s) is/are not decentered.
[0057] In FIGS. 1A-1C and 2-5, the major sides 108 and 110 of the
waveguide 102 were shown as being planar. However, as noted above,
in accordance with certain embodiments the major sides of the
waveguide are curved. This would enable, for example, the optical
waveguide to implemented as, or as a portion of, a curved visor of
a head mounted display.
[0058] In accordance with certain embodiment, the optical waveguide
102 (shown in FIGS. 2-5) is used as optical combiner that combines
the light corresponding to the image that is output from the
display engine 204 with light corresponding to an external scene.
Such an external scene is located on the side of the optical
waveguide 202 that is opposite the side on which the user's eye 214
is located. Such a configuration allows for an augmented reality
environment.
[0059] The optical waveguides described herein can be incorporated
into a see-through mixed reality display device system. The same
waveguide can be used to steer light of multiple different colors
(e.g., red, green and blue) associated with an image from the
input-coupler to the output-coupler. Alternatively, three
waveguides can be stacked adjacent to each other, with each of the
waveguides being used to steer light of a different colors (e.g.,
red, green or blue) associated with an image from its respective
input-coupler to its output-coupler. It would also be possible that
one waveguide handle light of two colors (e.g., green and blue) and
another waveguide handles light of a third color (e.g., red). Other
variations are also possible.
[0060] FIG. 6 is a high level flow diagram that is used to
summarize methods according to certain embodiments of the present
technology. Such methods, which are for use in a display device
system that includes a display engine and an optical waveguide, are
for preventing a ghost image from being formed by light
corresponding to an image that is reflected-back toward the display
engine from the optical waveguide. As explained above, the display
engine (e.g., 204) includes an image former (e.g., 206) and one or
more lens groups (e.g., 208), wherein each lens group of the one or
more lens groups including one or more lenses. If a lens group
includes a plurality of lenses, then the plurality of lenses of the
lens group share a same mechanical axis. As explained above, the
optical waveguide (e.g., 102) includes an input-coupler (112) and
an output-coupler (116), and may also include other components,
such as an intermediate-component 114), but is not limited
thereto.
[0061] In optics, a telecentric system is one in which the entrance
pupil and/or the exit pupil is located at infinity, and as a
consequence, principal rays for all field points are parallel to
the optical axis. Embodiments of the present technology described
above with reference to FIGS. 3-5 (and below with reference to FIG.
6) provide for non-telecentric systems that utilize one or more
lens groups of a display engine to avoid ghost images without
significantly increasing the design complexity compared to a
telecentric system. Embodiments of the present technology that tilt
the mechanical axis of at least two lens groups (relative to the
optical axis ray of light corresponding to an image produced by an
image former) take advantage of the fact that aberrations induced
by tilting one lens group can be compensated by tilting another one
of the lens groups in the opposite direction, e.g., as shown in
FIG. 4. A display engine designed using this approach is more
compact, easier to manufacture, assemble and align compared to, for
example, a display engine that provides for one or more
non-telecentric lens groups by decentering the aperture of one or
more lens groups.
[0062] Referring to FIG. 6, step 602 involves producing light
corresponding to an image using the image former of the display
engine, wherein the light corresponding to the image that is
produced by the image former has an optical axis ray (e.g., 223)
which is coincident with a principal ray of the light that
originates at a center of the image produced by the image
former.
[0063] Step 604 involves using the one or more lens groups of the
display engine to collimate the light corresponding to the image,
produced by the image former, and to output the light corresponding
to the image from the display engine, wherein at least one of the
lens group of the display engine has a mechanical axis that is
tilted relative to the optical axis ray of the light corresponding
to the image that is produced by the image former.
[0064] Step 606 involves coupling into the optical waveguide, using
the input-coupler of the optical waveguide, light corresponding to
the image that is output by the display engine.
[0065] Step 608 involves coupling out of the optical waveguide,
using the output coupler, light corresponding to the image that
that has traveled through the optical waveguide from the
input-coupler to the output-coupler at least in part by way of
total internal reflection (TIR).
[0066] Step 610 involves using at least one of the lens group of
the display engine, which has a mechanical axis that is tilted
relative to the optical axis ray of the light corresponding to the
image that is produced by the image former, to prevent a ghost
image from being formed by the light corresponding to the image
that is reflected-back toward the display engine from the optical
waveguide. Step 610 can be performed simultaneously with one or
more of steps 604, 606 and 608.
[0067] As noted above, the methods described with reference to FIG.
6 can be performed using an optical waveguide that includes at
least an input-coupler and an output-coupler, and may also include
an intermediate-component. Where the optical waveguide includes an
input-coupler (e.g., 112) and an output-coupler (e.g., 116), but
not an intermediate-component (e.g., 114), the input-coupler will
direct light that it couples into the optical waveguide toward the
output-coupler, and the output-coupler may provide one of
horizontal or vertical pupil expansion. Where the optical waveguide
also includes an intermediate-component, then the input-coupler can
be used to direct the light corresponding to the image (that is
coupled into the bulk-substrate of the optical waveguide) toward
the intermediate-component. The intermediate-component can be used
to perform one of horizontal or vertical pupil expansion and to
direct the light corresponding to the image towards the
output-coupler, and the output-coupler can be used to perform the
other one of horizontal or vertical pupil expansion. Additional
details of the methods summarized with reference to FIG. 7 can be
appreciated from the above discussion of FIGS. 1A, 1B, 1C and
2-5.
[0068] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the
claims.
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